I can contribute a couple of suggestions on valving, particularly check (one-way) valves. A swing check valve is about as simple and safe as you could get for tank to tank equalization. You can find them that seal bubble tight at zero back-pressure and open at as low a pressure as you chose. If you need hose-end ports, you'll probably want a ball-check valve. Their advantage is lower weight at the expense of higher pressure drop across the valve for a given size. Whichever, if you have a choice, use Viton, not Buna-N seals. Parker has a huge selection of all types of valves, with detailed specs. Aircraft Spruce has aviation-grade selector valves, etc., but, depending on your aversion to flames in the cockpit, they may seem expensive.
For serious engineering types,
Pressure Drop Online-Calculator PDA is a detailed online pressure drop calculator for every sort of hose radius, valve and fitting.
As an aside, and for what it's worth, Sunoco devised a simple and reliable automatic fire shut-off for their refinery gasoline storage tanks back in the '70s. It comprised a swing check valve with a lever arm, installed
backwards at the base of the tank outlet, and held open by a lead pin. It worked at least once that I know of. I don't know if it's been tried, but you might be able to do the same thing in the engine compartment using a spring loaded shut-off valve, locked open with a low melting-point pin- maybe even a zip tie. Shut off the fuel and/or vent the fire bottle when the link melts
And it occured to me that the multi unit compressor station at Lidy (SP?) Penn. that supplied half of New England with natural gas used one large Halon tank connected to a single hose that wrapped around the 15 or so turbines instead of a single bottle at each one. A fire or explosion at one unit would sever the line and vent the Halon at the point of origin. That might also work in an engine compartment to vent at a specific point instead of trying to fill an entire compartment volume, especially at speed.
Forgive me if these are already discredited automotive ideas. It's late, and I'm just remembering the ohl bidness back in the day,-when you spit on your palm and shook hands.
